1. Field of the Invention
This invention relates to electrical devices comprising conductive polymer compositions.
2. Introduction to the Invention
Conductive polymer compositions exhibiting PTC behavior, and electrical devices comprising them, are well known. Such electrical devices may comprise circuit protection devices, self-regulating strip heaters, or elongate cathodic protection devices. Reference may be made, for example, to U.S. Pat. Nos. 4,177,376, 4,330,703, 4,543,474 and 4,654,511 (Horsma, et al.), 4,237,441 (van Konynenburg, et al.), 4,238,812 and 4,329,726 (Middleman, et al.), 4,352,083 (Middleman, et al.), 4,317,027 (Middleman, et al.), 4,426,633 (Taylor), 3,351,882 (Kohler, et al.), 3,243,753 (Kohler), 4,689,475 (Matthiesen), 3,861,029 and 4,286,376 (Smith-Johannsen, et al.), French Patent Application No. 76 23707 (Moyer), and commonly assigned, copending applications, Ser. Nos. 141,989 (MP0715, Evans), 656,046 (MP0762, Jacobs, et al.), abandoned in favor of a file wrapper continuation Ser. No. 146,460 (filed Jan. 21, 1988) and published as European Patent Application No. 63,440 051,438 (MP0897-US5, Batliwalla, et al.) now U.S. Pat. No. 4,761,541 and 711,910 (MP1044, Au, et al.) now U.S. Pat. No. 4,724,417. The disclosure of each of the patents, publications, and applications referred to above is incorporated herein by reference.
Electrical devices with improved physical properties and improved electrical performance are achieved when the conductive polymer composition comprising the device is cross-linked. Such cross-linking can be accomplished through the use of chemical cross-linking agents or gamma or electron irradiation, or a combination of these. It is frequently true that ionizing irradiation generated by an electron beam results in the most rapid and cost-effective means of cross-linking.